The use of viticultural terroir units for demarcation of geographical indications for wine production in Stellenbosch and surrounds

[摘要] ENGLISH ABSTRACT:Due to increased consumer demand for products labelled by origin, and therequirement that these labels are a guarantee of both quality and product character,there is an increasing global focus on delimitation of denominations of origin. Theintegrity of denominations of origin and their defensibility can be ensured through theuse of terroirs as a basis for delimitation.The aims of this study were to establish the dominant environmental criteria thataffect the viticultural behaviour and wine character of two important cultivars(Cabernet Sauvignon and Sauvignon blanc) in the Stellenbosch Wine of OriginDistrict, to use an appropriate methodology to identify viticultural terroirs in this districtbased on these criteria and with the use of a geographic information system, andfinally to use these viticultural terroirs to identify denominations of origin within thesame area.A terroir can be defined as a grouping of homogenous environmental units, ornatural terroir units, based on the typicality of the products obtained. Identificationand characterisation of terroirs depends on knowledge of environmental parameters,the functioning of the grapevine and the characteristics of the final product. Fieldstudies, resulting in point data, are necessary to investigate the functioning of thegrapevine but in order for this information to be of use within zoning studies it mustbe placed in a spatial context.As a first phase in data acquisition, the Stellenbosch Wine of Origin District wascharacterised and natural terroir units were identified using existing digital data and ageographic information system. A natural terroir unit (NTU) can be defined as a unitof land that is characterised by relatively homogenous topography, climate,geological substrate and soil. A total of 1389 NTUs were identified in theStellenbosch Wine of Origin District (84 537 ha). The identified NTUs werehomogenous with respect to terrain morphological unit, altitude, aspect and soil type.Each of the identified units was further described with respect to the extent of theexpected sea breeze effect and, for certain of the soil types, the associated parentmaterial.As a second phase of data acquisition, a network of plots of Sauvignon blanc andCabernet Sauvignon were delimited in commercial vineyards in proximity to weatherstations and their viticultural and oenological response monitored for a period ofseven years.Regression tree analyses were performed on the complete data set and therelative importance of the environmental and management related variablesdetermined for each dependent variable. Excepting for scion clone, which had a highrelative importance for bunch mass of Sauvignon blanc and yield to pruning massindex of Cabernet Sauvignon, no other non-environmental variable included in theanalyses appeared to have a strong effect on grapevine performance and wine character. The performance of Cabernet Sauvignon was affected by the potassiumcontent of the subsoil and the climate of the season. The performance of Sauvignonblanc appeared to be related to soil texture, wind exposure and temperature, bothduring the green berry growth stage and the month prior to ripening. From the resultspresented, it appears that environmental parameters have an overriding effect on theperformance of both Cabernet Sauvignon and Sauvignon blanc, but that these twocultivars react differently to environmental stimuli.A knowledge-driven model used the rules generated in the regression treeanalyses to directly classify natural terroir units with respect to expected response ofCabernet Sauvignon and Sauvignon blanc in the Stellenbosch Wine of Origin District.The natural terroir units were thus grouped into terroir units that were homogenouswith respect to predicted viticultural and oenological response for each cultivar.The use of representative sites to determine the response of the grapevine to itsenvironment is time consuming and costly and limits terroir studies to researchrelated investigations. Vineyard managers were therefore surveyed with respect tothe functioning of established Sauvignon blanc vineyards in the Stellenbosch Wine ofOrigin District in an attempt to obtain the necessary data. Comparison of the datagenerated with these questionnaires to measured data in commercial vineyardssuggested that the vineyard managers were able to characterise the performance ofvineyards with respect to vigour, signs of drought stress and yield. Each vineyardwas mapped and the responses were linked to modelled environmental variables.Classification and regression trees were used to construct decision trees, whichcould be applied to environmental data in a geographic information system todetermine viticultural terroirs for production of Sauvignon blanc. These terroirs,although fewer, were comparable to those generated using field data.Data gathered during terroir studies, and the identified viticultural terroirs forCabernet Sauvignon and Sauvignon blanc, were used to revisit the boundaries of theStellenbosch Wine of Origin District and the Simonsberg-Stellenbosch ward.Modifications were proposed based on expected wine characteristics. Boundaries fortwo new wards in the Helderberg basin were proposed. It was also possible toidentify vineyards within a ward for the production of terroir specific wines.

[发布机构] Stellenbosch University